A valve suitable for fluids encountered in oil field operations (e.g., drilling mud) may comprise a valve body, a corresponding valve seat, and an elastomeric seal internal to a peripheral seal retention groove on the valve body. Such a valve may be mounted in the fluid end of a pump incorporating positive displacement pistons or plungers in multiple cylinders. Valve bodies of such valves move longitudinally between an open position (i.e., the valve body not contacting the valve seat) and a closed position (i.e., the valve body sealed against the valve seat). During such movement the valve body is typically guided to insure that a consistently effective seal may be repeatedly obtained against the valve seat.
Guide means for thus guiding the valve body take a variety of forms typically involving one or more structures extending from the bottom and/or top of the valve body. Note that a reference herein to the bottom or bottom portion of a valve body pertains to that portion comprising a surface intended for intermittent contact with a valve seat. The top or top portion of a valve body is longitudinally opposite the bottom or bottom portion. Examples of guide means include a stem-guided, full-open valve body design that incorporates a top guide stem and a bottom crow-foot guide on the valve body. On the other hand, a web-seat, stem-guided design incorporates top and bottom guide stems on the valve body. Other valve body designs may include guide means comprising, for example, a single top guide stem or a single bottom crow-foot guide. Guide means discussed herein typically comprise at least one longitudinal surface for guiding longitudinal valve body movement. Each such longitudinal surface may be continuous (e.g., the cylindrical surface of a guide stem) or discontinuous (e.g., the plurality of spaced-apart longitudinal surfaces present in a crow-foot guide).
However designed, the above valves are expensive to manufacture, especially the moving portion or valve body. Besides requiring finish machining to close tolerances for adequate sealing, such valve bodies must be made strong enough to resist significant distortion under load, which can result in leaks and/or fatigue failures of the valve body. Prior efforts to reduce distortion under load by strengthening such valve bodies have generally resulted in higher cost and/or heavier designs which exacerbate sealing problems and/or increase the stress of impact loading on components of the valve assembly.
Notwithstanding their relatively high cost, however, valve bodies having an integral seal retention groove have gained limited industry acceptance. Their relatively high strength and stiffness effectively counter valve body distortion about one or more axes radiating perpendicularly from the valve body's longitudinal axis of symmetry (radial axes). Distortion about radial axes is particularly a problem on valve bodies that mate with web seats. Cyclical high pressure applied to a valve body when it is sealed against a web seat tends to repeatedly force portions of the valve body into the spaces between the seat webs. The periphery of the disc-shaped area of the valve body (commonly called the flange) then tends to wrinkle like a cupcake paper, the number of wrinkles being equal to the number of seat webs.
While tending to resist distortion about radial axes, valve bodies having an integral seal retention groove generally incorporate an elastomeric seal insert that snaps into its peripheral seal retention groove. A typical “snap-on” seal insert comprises a portion of a toroidal structure such as a plastic or rubber ring that is sized to fit tightly, and thus sealingly, in the peripheral seal retention groove. When properly fitted, the elastomeric seal mates tightly with a corresponding valve seat even though the valve body may be slightly distorted and even if small particles carried by the pumped fluid may be trapped between sealing surfaces. Practical advantages of such a seal insert include extended valve life and improved valve performance, but proper fitting and sealing of the elastomeric ring on a valve body is often difficult in the field.
Some of the above problems associated with high machining and materials costs for the above valves, as well as those associated with seal movement and/or out-of-round seal placement, are reduced in valve bodies which incorporate a separate (removable) seal retention plate which commonly screws or bolts to the valve body to form at least part of one wall of a seal retention groove. Separate seal retention plates can be forged to near-net-shape, and they reduce the time required to correctly replace toroidal sealing rings. But they also raise valve fabrication costs and impose use restrictions. For example, they add excess weight to the moving valve body, aggravating impact loading stress. And a removable seal retention plate must be handled separately from the remainder of the valve body during manufacturing. Additionally, special skills and tools are required for proper assembly of a retention plate and seal ring on a valve body. Finally, the threads often used to secure a retention plate to a valve body are both expensive to machine and, because portions of the threads are relatively thin, they demand special protection during heat treatment. Nevertheless, removable seal retention plates are commonly used because such a plate, as well as the valve body to which it is attached in use, can be forged to a “near-net-shape” which requires relatively little finish machining to achieve a desired final shape.
Unfortunately then, even though forged valve bodies having integral seal retention groves are inherently stronger than designs requiring a removable seal retention plate, they are generally heavier, more expensive to make, and prone to failure due to seal movement and/or out-of-round seals. What is needed is a valve body having an integral seal retention groove without the disadvantages of high production costs, excessive weight, seal movement and/or out-of-round seal placement.
Attempts to overcome the cost disadvantage of forged valve bodies having integral seal retention grooves have included elimination of forgings altogether, substituting cast valve bodies instead. Though such castings may be produced to near-net-shape and thereby reduce machining costs, the generally higher cost of the casting process itself, compared to forging, has substantially eliminated any hoped-for reduction in overall cost. Additionally, cast valve bodies generally have lower impact strength compared to similarly shaped forgings. Thus, there is a need for a relatively light weight forged valve body incorporating the strength advantages of an integral seal retention groove and the efficiencies of initial formation to near-net-shape.